A. Field of the Invention
The present invention relates to a semiconductor device manufacturing method.
B. Description of the Related Art
To date, trench filling epitaxial technology has been known as a method of manufacturing a semiconductor device (hereafter referred to as a super junction semiconductor device) wherein the drift layer is a parallel p-n layer in which an n-type region with an increased impurity concentration and a p-type region are disposed alternately. Trench filling epitaxial technology is such that an n-type epitaxial film is formed on an n+ type silicon substrate, and a trench is formed in the n-type epitaxial film. A p-type epitaxial film is deposited on the n-type epitaxial film, including the inside of the trench, thus filling the trench with the p-type epitaxial film (for example, refer to JP-A-2007-096138).
Also, multilayer epitaxial technology is known as another method of forming a parallel p-n layer. Multilayer epitaxial technology is such that a parallel p-n layer is formed by epitaxial growth of an n-type semiconductor layer for forming an n-type drift region and selective ion implantation of a p-type impurity for forming a p-type region being repeatedly carried out (for example, refer to JP-A-2012-089736). Controllability of the impurity ratio (hereafter referred to as the p/n ratio) between the p-type region (p-type semiconductor layer) and n-type semiconductor layer of the parallel p-n layer is higher with the multilayer epitaxial technology than with the trench filling epitaxial technology.
A super junction MOSFET (insulated-gate field-effect transistor) is such that a parallel p-n layer is formed on a low resistance n+ type silicon substrate doped with arsenic (As) or antimony (Sb) (hereafter referred to as an arsenic doped substrate). As the arsenic doped substrate can be doped with an n-type impurity to a high concentration, it is possible to omit back surface processes, such as an implantation of ions into the substrate back surface and an annealing process in order to obtain an ohmic contact, and thus possible to reduce the number of steps.
However, when forming a parallel p-n layer by growing an epitaxial layer on the front surface of the arsenic doped substrate, so-called auto-doping, wherein arsenic in the arsenic doped substrate diffuses outward from the substrate back surface to the gas atmosphere and is taken into the epitaxial layer during growth, is likely to occur. As it is important to accurately control the parallel p-n layer p/n ratio when manufacturing a super junction MOSFET, there is a problem in that controllability of the parallel p-n layer p/n ratio decreases when auto-doping occurs.
A method whereby a silicon epitaxial layer is grown by low pressure chemical vapor deposition on the main surface of an underlying silicon wafer to which a dopant of arsenic, phosphorus, or boron is added to a concentration of 1.0×1019/cm3 or more, with the growth temperature in a range of 1,000 to 1,100 C, and moreover, with the pressure in a reaction chamber of a growth gas including SiH4 gas in a range of 1,999.83 Pa (15 Torr) to 2,666.44 Pa (20 Torr), has been proposed as a method of preventing auto-doping (for example, refer to JP-A-2009-176784).
By carrying out epitaxial growth at a low temperature of 1,100 C or less, as in JP-A-2009-176784, the impurity amount of arsenic diffusing outward from the arsenic doped substrate into the gas atmosphere is reduced. Also, by carrying out epitaxial growth in a low pressure atmosphere, as in JP-A-2009-176784, the flow of gas inside the chamber increases in speed, and arsenic diffusing outward from the arsenic doped substrate into the gas atmosphere is discharged to the exterior of the chamber before being taken into the epitaxial layer.
Also, a method whereby, as an aspect of a method of manufacturing an epitaxial wafer having a buried ion implanted layer, ion implantation such that a pre-implantation oxidation process is eliminated is realized by carrying out heat treatment for post-ion implantation crystal recovery in a hydrogen atmosphere, and as a result of an active oxide film formation process including pre-implantation oxidation carried out on an epitaxial layer being eliminated, the number of times heat is applied to the buried ion implanted layer decreases, and lateral diffusion is effectively suppressed, has been proposed as another method of preventing auto-doping (for example, refer to JP-A-2006-210934).